1. Field of the Invention
The present invention relates to a hybrid vehicle comprising a vehicle driving engine, and a motor, which can drive the engine or generate electric power. In particular, the present invention relates to a hybrid vehicle comprising a control device for controlling a DC/DC converter, used for supplying electric power to auxiliary machines of the vehicle in response to energy generated by the motor.
2. Description of the Related Art
Conventionally, various vehicles such as an EV (Electric Vehicle) or an HEV (Hybrid Electric Vehicle) acquire electric energy by rotating a three-phase alternating current motor for generating the three phase alternating current electric power by use of an inverter deriving the electric energy from a high voltage main battery (electric power storage cell). In, addition, vehicles are provided with a DC/DC converter for converting a high voltage (for example, 144V) of the main battery to 12V for supplying electric power to a control computer actuated by 12V or auxiliary machines (such as the cooling fan, air conditioner, fuel pump and so on), and an auxiliary battery for storing an electric power obtained by converting by a DC/DC converter.
However, in the above-described conventional vehicles, the DC/DC converter is always operated deriving energy from the main battery in order to actuate the auxiliary machines, and a problem arises in that the energy of the main battery cannot always be sufficiently utilized for rotating the motor for driving. In order to solve such a problem, a control device has been proposed in Japanese Unexamined Patent Application, First Publication No. Hei 7-79505. This control device comprises a vehicle travel detect signal generating device for generating a vehicle travel detect signal while the vehicle travels (vehicle is driving) and when the vehicle travels, the control device sets the output voltage of the DC/DC converter at a lower voltage (a voltage that cannot charge the auxiliary battery) which is lower than the output voltage at the time of vehicle stop. Consequently, a part of the electric power supplied to the DC/DC converter at the vehicle stop can be used for rotating the motor during the vehicle travels.
However, since the conventional control device merely distributes the electric power of the main battery, the conventional control device cannot cope with the output voltage drop of the battery caused by the rush current flowing in the auxiliary machines at the time of starting the DC/DC converter.
The above effect will be explained with reference to FIG. 6. As shown by line b in FIG. 6, for example, when the DC/DC converter is actuated, the output current of the DC/DC converter is rapidly increased due to the rush current to the auxiliary machines, as shown by line d in FIG. 6. The internal resistance of the main battery is normally in a range of 0.1 to 0.3 xcexa9, but the resistance increases at a level of 10 xcexa9 when the main battery is placed in a low temperature atmosphere. In addition, when a current flows rapidly in the DC/DC converter when the internal resistance is high, the output voltage of the main battery may cause a large voltage drop, as shown by line e in FIG. 6.
As a result, depending upon the increased internal resistance, the output voltage of the main battery may be reduced to below the lower limit voltage, shown by line e in FIG. 6, of the main battery (power storage cell). Excessive reduction of the output voltage causes an overdischarge of the battery, degradation of the battery, and deterioration of the service life of the battery. The control battery voltage, shown by line c in FIG. 6, represents the voltage applied to the auxiliary battery. As shown by line d in FIG. 6, even when the output current from the DC/DC converter increases rapidly, since the rapid increase is caused by the rush current, the voltage applied to the auxiliary battery increases gradually.
In order to solve the aforementioned problem, a technique to prevent the excessive voltage drop of the main battery has been proposed in the hybrid vehicle comprising a travel driving engine and a motor which drives the engine or which can generate electric energy. The technique to prevent the excessive voltage drop in the hybrid vehicle is carried out such that by using the motor as a motor generator, the discharge from the main battery is reduced to be as low as possible by controlling generation of the motor-generator driven by the engine in response to the input current to the DC/DC converter.
However, the above-described technique encounters a limit. This is, associated with the late response of the secondary air valve used for stabilizing the engine rotation when the engine is in the idle state, even when it is desired to compensate for the electric energy consumed by the DC/DC converter by one time generation by the motor generator, the engine output does not follow the increase of the generation torque of the motor generator, which results in causing the engine encountering stall or rotation fluctuation. When the generation torque of the motor generator is slowly increased so as to meet the late response of the secondary air valve, it will take time to convert the energy generated by the motor generator to the output voltage of the DC/DC converter, and, as a result, insufficient power will be compensated by the discharge of the battery, causing further voltage drop of the main battery.
The present invention has been made to solve the aforementioned problems, and it is the object of the present invention to provide a hybrid vehicle and a control method therefor which, while maintaining the stabilized idle rotation of the engine, is capable of preventing the temporary voltage drop of the battery by controlling the discharge of the battery at the time of starting the DC/DC converter at low temperatures.
The first aspect of the present invention provides a hybrid vehicle comprising an engine (for example, an engine 7 in the embodiment) for driving the vehicle, and a motor (for example, a motor generator 6 in the embodiment) for driving the engine or for generating electric energy, a battery (for example, a high voltage battery 1 in the embodiment), a DC/DC converter (for example, a output variable DC/DC converter 2 in the embodiment) for supplying energy to the auxiliary machines (for example, a controller computer and auxiliary machines 3 in the embodiment), a temperature detecting device (for example, a temperature sensor 11 in the embodiment), and an output voltage increasing device (for example, motor controllers 8 and 21 in the embodiment), when the temperature of the battery is below a predetermined temperature, the output voltage increasing device sets the output voltage at a predetermined voltage and starting the DC/DC converter, and, after starting the DC/DC converter, and gradual increases the output voltage of the DC/DC converter from the predetermined voltage.
By constituting the hybrid vehicle as described above, when the engine is in the idle state and the electric energy generated by the motor is low, and when the temperature of the battery is below a predetermined temperature, the DC/DC converter is activated at a low output voltage, and the output voltage of the DC/DC converter is increased gradually from the voltage at the time of activation so that the electric power consumed by the DC/DC converter can be increased gradually.
According to the second aspect of the present invention, the hybrid vehicle comprising an engine (for example, an engine 7 in the embodiment) for driving the vehicle and a motor (for example, a motor generator 6 in the embodiment) for driving of the engine or for generating electric power, and a battery (for example, a high voltage battery 1 in the embodiment), which is charged by electric power generated by the motor, a DC/DC converter (for example, a output variable DC/DC converter 2 in the embodiment), capable of outputting a variable output voltage, and outputting a control voltage for controlling auxiliary machines of the vehicle by decreasing the voltage of the battery, a temperature detecting device (for example, a temperature sensor 11 in the embodiment) for detecting a temperature of the battery; and an output voltage switching control device (for example, a motor controller 8 and 21 in the embodiment), which activates the DC/DC converter by setting the output voltage of the DC/DC converter at a first voltage when the temperature of the batter is below the predetermined temperature, and which carries out a control operation to switch the output voltage from the first voltage value to a second voltage value, which is higher than the first voltage.
By constituting the hybrid vehicle as described above, when the engine is in the idle state and the electric energy generated by the motor is low, and when the temperature of the battery is below a predetermined temperature, the DC/DC converter is activated at a low output voltage, and then the output voltage of the DC/DC converter is switched to a higher voltage so that the electric power consumed by the DC/DC converter can be increased in a stepwise manner.
According to the third aspect of the present invention, in the above hybrid vehicle, after activating the DC/DC converter, the output voltage increasing device gradually increases the amount of electric power generated by the motor in response to the output response characteristic of the engine, and gradually increases the output voltage of the DC/DC converter in response to the increase amount of electric power generated by the motor.
By constituting the hybrid vehicle as described above, when the engine is in the idle state and the electric energy generated by the motor is low, and when the temperature of the battery is below a predetermined temperature, the DC/DC converter is activated at a low output voltage, and while the amount of electric power generation is increased at a speed which does not disturb the idle rotation of the engine, the output voltage of the DC/DC converter is gradually increased, so that it becomes possible to gradually increase the electric power consumed at the output side of the DC/DC converter by an increasing amount of electric power generated by the motor.
According to the fourth aspect of the present invention, after the DC/DC converter is activated, the output voltage switching control device gradually increases the amount of electric power generated by the motor in response to the output response characteristic of the engine, and switches the output voltage of the DC/DC converter from the first voltage to the second voltage.
By constituting the hybrid vehicle as described above, the DC/DC converter is activated at a low output voltage when the engine is in the idle state and the electric power generated by the motor is low, and the output voltage of the DC/DC converter is switched from a low voltage to a high voltage while the output voltage of the DC/DC converter is increased gradually at a low speed so as not to disturb the idle rotation of the engine; thereby the electric power consumed at the output side of the DC/DC converter can be increased at the state, where the electric power generated by the motor is ensured.
According to the fifth aspect of the present invention, the hybrid vehicle further comprising a electric power comparison device (for example, the high voltage electric power information acquisition portion 14, and the low voltage electric power information acquisition portion 17, and steps S5 to step S7 in the embodiment) for comparing between the electric power generated by the motor and the electric power consumed by the DC/DC converter, and when it is determined by the electric power comparison device that the electric power generated by the motor is equivalent to the electric power consumed by the DC/DC converter, the output voltage switching control device carries out a control operation to switch the output voltage of the DC/DC converter from the first voltage to the second voltage.
By providing the hybrid vehicle as described above, the amount of electric power generated by the motor can be dynamically controlled so as to meet the electric power consumed by the DC/DC converter. It is also possible to increase the electric power to be consumed at the output side of the DC/DC converter by switching the output voltage of the DC/DC converter from the low voltage at the time of start to a higher voltage while the electric power generated by the motor is sufficiently preserved.
According to the sixth aspect of the present invention, the hybrid vehicle further comprising a torque comparison device (for example, the high voltage electric power information acquisition portion 14, and the low voltage electric power information acquisition portion 17, the rotation sensor 19, and steps S15 to step S19 in the embodiment) for comparing between the electric power generation torque by the motor and the target electric power torque, and when it is determined by the torque comparison device that the power generation torque by the motor is equivalent to the target power generation torque, the output voltage switching control device carries out a control operation to switch the output voltage of the DC/DC converter from the first voltage to the second voltage.
By constituting the hybrid vehicle as described above, the output voltage of the DC/DC converter can be switched from the low voltage at the time of activation to the higher voltage when it is determined that the electric power obtained by generation of the motor by the comparison between the power generation torque of the motor and the target power generation torque for obtaining electric power consumed by the DC/DC converter, so that it is possible to increase the amount of electric power to be consumed at the output side of the DC/DC converter in the state where the electric power by the motor is sufficiently reserved.
According to the seventh aspect of the present invention, in the above hybrid vehicle, the torque comparison device calculates the target power generation torque from the electric power consumed by loads connected to the DC/DC converter and from a number of rotation of the motor.
By constituting the hybrid vehicle as described above, the torque comparison device is capable of dynamically calculating the target power generation torque in conformity with the change of the electric power consumed at the output side of the DC/DC converter.
The eighth aspect of the present invention provides a method of controlling a hybrid vehicle is provided which comprises an engine (for example, an engine 7 in the embodiment) for driving the vehicle, a motor (for example, a motor generator 6 in the embodiment) for driving the engine or for generating electric power, a battery (for example, a high voltage battery 1 in the embodiment), to be charged by electric power generated by the motor; a DC/DC converter (for example, an output variable DC/DC converter 2 in the embodiment), capable of outputting a variable output voltage, and outputting a control voltage for controlling auxiliary machines of the vehicle (for example, a control computer and auxiliary machines 3 in the embodiment) by depressing the voltage of the battery, and a temperature detecting device (for example, a temperature sensor 11 in the embodiment) for detecting a temperature of the battery, wherein the method of controlling the hybrid vehicle further comprises; a control step for activating the DC/DC motor while setting the output voltage of the DC/DC converter at a predetermined voltage, when the temperature of the battery is below a predetermined temperature, and a control step, after the DC/DC converter has been activated, for gradually increasing the output voltage of the DC/DC converter from the predetermined voltage.
The ninth aspect of the present invention provides a method of controlling a hybrid vehicle comprising an engine (for example, engine 7 in the embodiment) for driving the vehicle, a motor (for example, motor generator 6 in the embodiment) for driving of the engine and for generating electric power, a battery to be charged by electric power generated by the motor; a DC/DC converter, capable of outputting a variable output voltage, and outputting a control voltage for controlling auxiliary machines of the vehicle by depressing the voltage of the battery, and a temperature detecting device for detecting a temperature of the battery, wherein the method of controlling the hybrid vehicle comprises a step for activating the DC/DC motor while setting the output voltage of the DC/DC converter at a first voltage, when the temperature of the battery is below a predetermined temperature, and a step, after the DC/DC converter has been activated, for switching the output voltage of the DC/DC converter from the first voltage to the second voltage which is higher than the first voltage.